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I have problem getting the output resistance of this current mirror. How should I draw the small signal circuit and derive the output resistance equation?

  • 1
    \$\begingroup\$ The procedure for drawing the small signal equivalent circuit is the same as for a standard current mirror or any other circuit really. \$\endgroup\$ – Bimpelrekkie Dec 11 '18 at 14:23
  • \$\begingroup\$ First draw a standard 2-FET current mirror with all the input and output biasing, then insert a test current (AC, so is small signal) to the output. \$\endgroup\$ – analogsystemsrf Dec 11 '18 at 14:26
  • \$\begingroup\$ Hi I have tried using a test source. But I still can’t manage to get output resistance equation given \$\endgroup\$ – Jalin Yu Dec 11 '18 at 14:49
  • \$\begingroup\$ Must be a current-test-source. And your model must include the output resistance of the FET (the lambda effect, or in bipolars its called the Early Voltage Effect). What is the bias point for the output transistor? 10uA and 1.5 volts? \$\endgroup\$ – analogsystemsrf Dec 11 '18 at 15:00
  • \$\begingroup\$ If we were to ignore the body effect and the bias resistor? The circuit is designed in mos. If we were to get the output resistance, we need to have the small signal circuit. Then apply test source, let’s say Vx at the output. Then Ix follow from Vx into the circuit. Ro is obtained by Vx/Ix. I know the procedure but I can’t get the output resistance equation. The circuit analysis of the small signal model is troubling me. \$\endgroup\$ – Jalin Yu Dec 11 '18 at 15:10

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